The invention relates to a magnetic disk apparatus and, more particularly, to a mechanism.structure for precisely positioning a head to write and read information to a predetermined position over a magnetic disk on which information is stored.
Hitherto, a voice coil motor has been used as an actuator to move a magnetic head to a desired position over a disk. According to this method, however, there is a limitation to improve a positioning precision. As a method of performing a positioning operation of a higher precision, therefore, a construction such that a second actuator to finely adjust the position of the magnetic head is arranged between the voice coil motor and the magnetic head has been proposed.
For example, according to a structure of a second actuator disclosed in JP-A-9-73746, total four piezoelectric elements are adhered to the surface of an elastic member to support a magnetic head, namely, two piezoelectric elements are adhered onto the upper surface of the elastic member, two piezoelectric elements are adhered onto the lower surface of the elastic member, and by applying a voltage to the piezoelectric element, the element is contracted and extended, thereby finely adjusting the position of the magnetic head.
The second actuator in the foregoing conventional technique has two problems which will be explained hereinbelow.
The first is a problem of a leakage displacement which simultaneously occurs in the direction perpendicular to the actuator surface when the second actuator is deformed in the positioning direction of the magnetic head. The leakage displacement is caused due to a difference between distortions of the elastic member and a piezoelectric flat plate. Since the leakage displacement causes a gap between the magnetic head and the magnetic disk to be changed, a reading sensitivity or writing sensitivity in a magnetic disk apparatus is fluctuated. In the worst case, a collision of the magnetic head and the magnetic disk is also caused.
The second is a problem regarding the productivity such that four piezoelectric flat plates are adhered to the elastic member for supporting the magnetic head. According to the adhering operation, particularly, in case of fine parts having a size of millimeter, the productivity is low and it is very difficult to specify the position where they are adhered with high precision.
In consideration of those technical problems, it is an object of the invention to provide a second actuator in which a leakage displacement in a direction other than the positioning direction is small and a productivity is high, thereby providing a magnetic disk apparatus which can inexpensively realize a high recording density.
To accomplish the above object, according to the invention, there is provided
(1) a magnetic disk apparatus comprising: a magnetic head for writing and reading information; a magnetic disk on which information is stored; an elastic member for supporting the head; a fixed member for supporting the elastic member; a first actuator for coarse movement for moving the magnetic head to a predetermined position over the magnetic disk; and a second actuator for fine movement arranged between the first actuator and the magnetic head,
wherein the second actuator is a plate-shaped structure constructed by one or a plurality of laminated piezoelectric flat plates having electrodes on an upper surface and a lower surface and having therein two or more polarization regions and is arranged in a manner such that both upper surfaces or both lower surfaces of the fixed member and the elastic member are bridged by using the upper surface or lower surface of the second actuator as a plate-shaped structure.
(2) The second actuator is a plate-shaped structure constructed by one or a plurality of laminated piezoelectric flat plates each of which is made of a material having piezoelectric performance and has electrodes on an upper surface and a lower surface and is constructed in a manner such that the electrode of at least one of the upper and lower surfaces in the electrodes formed thereon is separated into two or more electrodes, the piezoelectric flat plate has therein a region which is not polarized and two or more polarization regions which are separated by a part of the non-polarized region and polarized in the thickness direction of the piezoelectric flat plate, and by applying an electric field to the two or more polarization regions in the piezoelectric flat plate in the thickness direction of the piezoelectric flat plate by using the electrodes formed on the upper and lower surfaces of the piezoelectric flat plate, the piezoelectric flat plate is deformed in the in-plane direction of the piezoelectric flat plate.